1. Field of the Invention
This invention relates to a scanning rate converter for a television signal , which is adapted for converting a scanning rate to a scanning rate of 1/N to output it, and more particularly to a scanning rate converter adapted for generating a television signal of a reference frequency from a high speed television signal having a frequency N times greater than that of the reference frequency of a television signal in which odd and even fields are generated one after another in correspondence with respective intervals of even fields and odd fields of the television signal having the reference frequency, and the total number of the odd fields and even fields is equal to N (N is an odd number).
2. Description of The Prior Art
As for a television signal of the standard television system, a scanning period of one frame is prescribed. For example, in the case of the NTSC system, since the field frequency is 60 Hz, it is unable with a television camera of the NTSC system to capture a moving object varying at a speed higher than 1/60 sec. In view of this, as disclosed in the Japanese Laid Open Patent Application NO. 17292/84 publication, for example, there is provided a high speed actual or real image recorder in which a television camera having a scanning rate N times greater than that of the standard television system is used to pick up an object image to record, in a multi channel form, image pickup output signals into a video tape recorder.
In order to monitor, by using an image monitor, an image pickup output by a television camera having an N-tuple scanning rate used in such a high speed actual or real image recorder, it is necessary to use a special image monitor of the N-tuple scanning rate, or to use a scanning rate (speed) converter for converting a scanning rate of an image pickup output by the television camera to a scanning rate of the standard television system.
Meanwhile, the television camera is adapted to carry out an imaging operation synchronous with a reference television signal for external synchronization. With a television camera of the N-tuple scanning rate, a television signal of the N-tuple scanning rate is generated with the reference television signal as a reference. A scanning rate converter adapted for converting a scanning rate of an image pickup output by such a television camera of the N-tuple scanning rate to a scanning rate of the standard television system requires a reference television signal of a basic (standard) scanning rate. For this reason, an input terminal for a high speed television signal of the N-tuple scanning rate and an input terminal for a reference television signal of the basic scanning rate must be juxtaposed, disadvantageously resulting in an increased number of terminals for external connection.
Further, in the case of converting a scanning rate of an image pickup output by a television camera of the N-tuple scanning rate to a scanning rate of the standard television system, if a scheme is merely employed as shown in FIG. 1, for example, to expand three times the time base of image outputs every three fields of image pickup outputs by a television camera of the treble scanning rate to use them as video signals of respective fields of a television signal of the standard television system, there would occur, between respective fields, time differences corresponding to a time period of three fields in the television signal of the treble scanning rate. For this reason, there is the problem that the contour of a moving picture might take a form of stair-steps, or motion or movement of a picture might fail to be smooth.